STEREO spacecraft to image solar blasts in glorious 3-D

Blasts of energetic particles from the Sun will soon be visible barrelling towards Earth in glorious 3-D, thanks to a pair of NASA spacecraft called STEREO. The mission should help researchers to predict which solar storms could endanger astronauts or damage satellites.

Both STEREO (Solar Terrestrial Relations Observatory) spacecraft are scheduled to launch aboard the same Delta 2 rocket from Florida's Cape Canaveral Air Force Station on 26 May 2006.

Once in space, they will split up to observe the Sun from different angles, capturing images in 3-D. People gauge depth in the same way, using the slightly different perspective from each eye.

Two months after launch, both spacecraft will swing by the Moon and one - called B for "behind" - will arrive at its destination, a point about 22° behind the Earth in its orbit. Its own orbit will be farther from the Sun than Earth's, taking about 387 days to complete.

About a month after that, the other spacecraft - called A for "ahead" - will fly by the Moon again. It will then reach its intended orbit, about 22° in front of the Earth and closer to the Sun, taking 347 days to orbit.

Mass ejections

The combined observations from these two locations should allow researchers to monitor the trajectory of eruptions of charged particles from the Sun, called coronal mass ejections (CMEs). If they are on a collision course with the Earth, they can endanger space-walking astronauts, damage spacecraft and disrupt power grids on the ground.

Each spacecraft will monitor the Sun with four instrument packages. One, called SECCHI, carries four instruments that will image the Sun at a range of wavelengths.

Two others, called IMPACT and PLASTIC, will measure the particles and their associated magnetic fields directly as they sweep over the spacecraft. The fourth package, called SWAVES, will study radio emissions produced in the shock wave as the CME particles plough into slower-moving particles from the Sun.

Space weather

Each spacecraft also carries a beacon that will transmit data in real-time to project scientists and to the US National Oceanic and Atmospheric Association's Space Environment Center in Boulder, Colorado. Eventually, this data will be used to forecast space weather, says Kaiser.

"Everything until now has been looking right at the Sun, but all of a sudden there's data from the side," he said at a press briefing at the American Geophysical Union in San Francisco, California. "This will be a whole big change."

Data from other orbiting spacecraft, such as SOHO, and observations from Earth will also be used to augment STEREO's vision, providing an unprecedented look at the relationship between the Sun and the Earth.

"Just like we can't measure ocean current with one - or even several - buoys, we need many observations and imaging to really understand this coupled system," says STEREO programme scientist Lika Guhathakurta of NASA.

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One stereo spacecraft will orbit the Sun ahead of the Earth, one behind, in order to generate a 3-D view (Image: JHU Applied Physics Laboratory)